Coronary artery disease is the leading cause of death in the USA. The major goal of treating myocardial infarction is to restore blood flow to the heart by opening the occluded coronary artery and reperfusing the heart. But even after the vessel is opened, about 25% of patients with a myocardial infarction do not have myocardial perfusion at the tissue level, and they have a much worse prognosis. Lack of myocardial perfusion after therapy is referred to as the no-reflow phenomenon. The no-reflow phenomenon is caused by microvascular obstruction: the large coronary artery is patent but the small capillaries are blocked with clumps of leukocytes and platelets. The pathogenesis of microvascular obstruction is complex and not well understood. We propose that endothelial exocytosis plays a pivotal role in microvascular obstruction. Our theory is that ischemia and reperfusion trigger endothelial release of granules. The secreted contents of endothelial granules then cause neutrophil adherence and platelet activation, leading to microvascular obstruction. Exocytosis is the regulated secretion of messenger molecules from cells. Exocytosis is fundamental to cell biology, but our understanding of exocytosis in other mammalian cells is limited. The overall goal of my lab is to understand pathways of exocytosis in the human vasculature. We recently discovered that endothelial exocytosis plays a major role in ischemia and reperfusion injury. We invented peptides that target the exocytic machinery, blocking endothelial exocytosis, limiting microvascular obstruction, and decreasing ischemia- reperfusion injury. Our new preliminary data now show that VAMP8 regulates endothelial exocytosis. The goal of this project is to characterize the role of VAMP8 in exocytosis and microvascular obstruction. Our hypothesis is that VAMP8 mediates endothelial exocytosis, vascular inflammation, and microvascular obstruction. In this proposal we will define the role of VAMP8 in endothelial exocytosis. We will determine the subcellular location of VAMP8 and identify its interaction partners in endothelial cells. Next we will characterize the domains of VAMP8 that mediate interactions with VAMP8 partners, and develop peptides which block these domains. This aim will reveal the molecular role of VAMP8 in the exocytic machinery of endothelial cells. Next we will define the role of VAMP8 in vascular inflammation and microvascular obstruction in vivo. We will characterize the effect of VAMP8 upon endothelial exocytosis in vivo. We will measure the effect of VAMP8 upon leukocyte trafficking in mice. We will then measure the effect of VAMP8 upon microvascular obstruction, using mice that lack VAMP8 in a model of myocardial ischemia-reperfusion. Finally we will test that ability of peptides to block VAMP8 and limit microvascular obstruction. This aim will reveal how VAMP8 affects microvascular obstruction.